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FS-1996-05-03-LaRC
May 1996

The Earth Radiation Budget Experiment (ERBE):

Using Satellites to Better Understand the Earth's Climate

The Earth Radiation Budget Experiment (ERBE) is designed around
three Earth-orbiting satellites: the NASA Earth Radiation Budget
Satellite (ERBS), and two NOAA satellites. The data from these
satellites is being used to study the energy exchanged between the
Sun, the Earth and space. The ERBE instrument aboard ERBS, launched
from the Space Shuttle Challenger in October 1984 (STS-41G), had
the primary goals of determining, for at least one year: the
Earth's average monthly energy budget and its monthly variations,
the seasonal movement of energy from the tropics to the poles, and
the average daily variation in the energy budget on a regional
scale (data every 160 miles). All of these first year goals were
met, and the ERBE instrument continues to provide valuable data
more than 10 years later.

ERBE has helped scientists world-wide better understand how
clouds and aerosols, as well as some chemical compounds in the
atmosphere (so-called "greenhouse" gases), affect the Earth's daily
and long-term weather (the Earth's "climate"). In addition, the
ERBE data has helped scientists better understand something as
simple as how the amount of energy emitted by the Earth varies from
day to night. These diurnal changes are also very important aspects
of our daily weather and climate.

Balancing the Earth's Radiation Budget

The Earth's daily weather and climate is controlled by the balance
between the amount of sunlight received by the Earth (both its
surface and atmosphere) and the amount of energy emitted by the
Earth into space. Scientists have been trying for decades to
understand this critical balance - to understand the budget of
incoming and outgoing energy, called the radiation budget. Much
like our own financial budgets of incoming and outgoing money, the
Earth's climate works better when the energy budget is balanced.

The instruments aboard the ERBE satellites measure the amount of
solar energy received by the Earth, the energy emitted by the Earth
into space, and the amount of solar radiation which is reflected
into space. The energy received from the sun is at short
wavelengths while the energy emitted by the surface of the Earth
and clouds is long wavelength radiation. Some of the shortwave
radiation from the sun is reflected back into space by water vapor,
ozone, clouds and small particles in the atmosphere called
aerosols. Gases which absorb the longwave radiation emitted by the
Earth are known as "greenhouse" gases. Increases in the amount of
greenhouse gases can lead to a warming of the atmosphere, which
can, in turn, cause changes in the Earth's daily and long-term
weather ("climate").

Clouds and Water Vapor Affect Climate

One of the most intriguing questions facing climate modelers today
is how clouds affect the climate and vice versa. Understanding
these effects requires a detailed knowledge of how clouds absorb
and reflect both incoming shortwave solar energy and outgoing
longwave Earth radiation. Analyses of the ERBE data have shown that
clouds which form over water are very different than clouds which
form over land. These differences affect the way clouds reflect
sunlight back into space and how much longwave energy from the
Earth the clouds absorb and re-emit.

For example, ERBE has provided data for investigating the
significant decrease in the Earth's emitted radiation due to
increased cloudiness over the equatorial Pacific Ocean during El
Nino events, which occur when the ocean becomes considerably warmer
than normal. The ERBE results are very important to scientists
working to improve computer models for climate and weather
prediction.

Water vapor in the atmosphere also affects our daily weather and
climate, though scientists are only beginning to understand how
these complex mechanisms work. Water vapor acts like a greenhouse
gas, absorbing outgoing longwave energy. Because water vapor also
condenses to make clouds, an increase in water vapor in the
atmosphere also may increase the amount of clouds in the
atmosphere. Using the ERBE data, scientists have begun to
understand the effects of water vapor and how its variability
affects clouds and ultimately, the energy balance of the Earth.

ERBE's
Future

During the past 10 years, ERBE data has been invaluable for
scientists studying the energy interactions between the Sun, clouds
and Earth, and the effects of these interactions on our weather and
climate. ERBE satellite measurements have providedments new
information on Earth's radiation at the top of the atmosphere
including the important radiative effects of clouds on our climate.

The Clouds and the Earth's Radiant Energy System (CERES), based on the highly successful ERBE, is
currently being developed. CERES will extend the important ERBE
measurements to include the top of the atmosphere, in the
atmosphere, and global surface radiation, which are critical for
advancing our understanding of the Earth's total climate system and
improving climate prediction models. CERES will be flown on
multiple satellites starting with a launch on the Tropical Rainfall
Measuring Mission in 1997, followed by a launch on the Earth
Observing System (EOS)-AM satellite in 1998 and the EOS-PM
satellite in 2000.